/*
 * Copyright (c) 2007-2012, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
/*
 * Copyright 1999-2004 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id: ObjectPool.java,v 1.2.4.1 2005/09/15 08:15:50 suresh_emailid Exp $
 */
package com.sun.org.apache.xml.internal.utils;

import java.util.ArrayList;

import com.sun.org.apache.xml.internal.res.XMLErrorResources;
import com.sun.org.apache.xml.internal.res.XMLMessages;
import com.sun.org.apache.xalan.internal.utils.ObjectFactory;

/**
 * Pool of object of a given type to pick from to help memory usage
 * @xsl.usage internal
 */
public class ObjectPool implements java.io.Serializable {
    static final long serialVersionUID = -8519013691660936643L;

    /** Type of objects in this pool.
     *  @serial          */
    private final Class objectType;

    /** Stack of given objects this points to.
     *  @serial          */
    private final ArrayList freeStack;

    /**
     * Constructor ObjectPool
     *
     * @param type Type of objects for this pool
     */
    public ObjectPool(Class type) {
        objectType = type;
        freeStack = new ArrayList();
    }

    /**
     * Constructor ObjectPool
     *
     * @param className Fully qualified name of the type of objects for this pool.
     */
    public ObjectPool(String className) {
        try {
            objectType = ObjectFactory.findProviderClass(className, true);
        } catch (ClassNotFoundException cnfe) {
            throw new WrappedRuntimeException(cnfe);
        }
        freeStack = new ArrayList();
    }

    /**
     * Constructor ObjectPool
     *
     *
     * @param type Type of objects for this pool
     * @param size Size of vector to allocate
     */
    public ObjectPool(Class type, int size) {
        objectType = type;
        freeStack = new ArrayList(size);
    }

    /**
     * Constructor ObjectPool
     *
     */
    public ObjectPool() {
        objectType = null;
        freeStack = new ArrayList();
    }

    /**
     * Get an instance of the given object in this pool if available
     *
     *
     * @return an instance of the given object if available or null
     */
    public synchronized Object getInstanceIfFree() {

        // Check if the pool is empty.
        if (!freeStack.isEmpty()) {

            // Remove object from end of free pool.
            Object result = freeStack.remove(freeStack.size() - 1);
            return result;
        }

        return null;
    }

    /**
     * Get an instance of the given object in this pool
     *
     *
     * @return An instance of the given object
     */
    public synchronized Object getInstance() {

        // Check if the pool is empty.
        if (freeStack.isEmpty()) {

            // Create a new object if so.
            try {
                return objectType.newInstance();
            } catch (InstantiationException ex) {
            } catch (IllegalAccessException ex) {
            }

            // Throw unchecked exception for error in pool configuration.
            throw new RuntimeException(XMLMessages.createXMLMessage(XMLErrorResources.ER_EXCEPTION_CREATING_POOL, null)); //"exception creating new instance for pool");
        } else {

            // Remove object from end of free pool.
            Object result = freeStack.remove(freeStack.size() - 1);
            return result;
        }
    }

    /**
     * Add an instance of the given object to the pool
     *
     *
     * @param obj Object to add.
     */
    public synchronized void freeInstance(Object obj) {

        // Make sure the object is of the correct type.
        // Remove safety.  -sb
        // if (objectType.isInstance(obj))
        // {
        freeStack.add(obj);
        // }
        // else
        // {
        //  throw new IllegalArgumentException("argument type invalid for pool");
        // }
    }
}
